Method for producing steel sheet, method for producing magnetic domain refined grain-oriented electrical steel sheet, facility for producing steel sheet, and facility for producing magnetic domain refined grain-oriented electrical steel sheet

Abstract

To provide a method and a facility for producing a steel sheet by which gas adsorbed on the surface of the steel sheet carried into a vacuum tank can be removed without heating and / or cooling the steel sheet in the production facility having the vacuum tank through which the steel sheet is passed.SOLUTION: In a method for producing a steel sheet, in a production line having a vacuum tank through which a steel sheet is passed, the steel sheet is irradiated with far ultraviolet rays having wavelengths below 200 nm at integrated irradiance of 150 mJ / cm2 or more on the upstream side of the vacuum tank. A facility for producing a steel sheet includes the vacuum tank through which a steel sheet passes, and a far ultraviolet irradiation device that is installed upstream of the vacuum tank and irradiates the steel sheet with far ultraviolet rays.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a steel sheet, a method for manufacturing a magnetic domain refinement grain-oriented electrical steel sheet, a steel sheet manufacturing facility, and a magnetic domain refinement grain-oriented electrical steel sheet manufacturing facility. [Background technology]

[0002] Grain-oriented electrical steel, a type of steel sheet, is primarily used as the iron core of transformers. Grain-oriented electrical steel sheets are required to have excellent magnetic properties, particularly low iron loss. To achieve this, it is important to highly align the secondary recrystallized grains in the steel sheet with the (110)

[0001] orientation (Goss orientation) and to reduce impurities in the product. Furthermore, because there are limits to controlling crystal orientation and reducing impurities, technologies have been developed to reduce iron loss by forming grooves or introducing local strain into the steel sheet surface, thereby introducing magnetic flux nonuniformity and refining the magnetic domain width (hereinafter referred to as magnetic domain refinement processing). Hereinafter, grain-oriented electrical steel sheets that have undergone magnetic domain refinement processing will also be referred to as magnetic domain refined grain-oriented electrical steel sheets.

[0003] As a method for forming grooves in a steel sheet, for example, an electrolytic etching method (Patent Document 1) has been proposed, in which grooves are formed on the surface of the steel sheet by electrolytic etching. Other proposed methods include a laser method (Patent Document 2) in which a high-power laser is used to locally melt and vaporize the steel sheet, and a gear press method (Patent Document 3) in which a gear-shaped roll is pressed against the steel sheet to create an indentation. Furthermore, as a method for introducing local strain into a steel sheet, for example, a method for introducing local thermal strain by irradiating the steel sheet with an electron beam (Patent Document 4) and a method for introducing local thermal strain by irradiating the steel sheet with a plasma flame (Patent Document 5) have been proposed.

[0004] As described above, magnetic domain refinement processes can be broadly divided into two types: a method of directly forming grooves in steel sheet, and a method of introducing thermal strain into steel sheet. The former is called heat-resistant magnetic domain refinement process because the magnetic domain refinement effect is not lost even when stress relief annealing is performed after core forming. On the other hand, the latter is called non-heat-resistant magnetic domain refinement process because the effect of introducing thermal strain is lost due to stress relief annealing.

[0005] In the heat-resistant magnetic domain refinement process, linear grooves are directly introduced into the steel sheet, but this process is known to degrade the magnetic permeability of the steel sheet. In contrast, in the non-heat-resistant magnetic domain refinement process, localized strain is introduced, so no degradation of magnetic permeability occurs. Therefore, in transformers using stacked cores that do not require annealing in the manufacturing process, steel sheets that have undergone the non-heat-resistant magnetic domain refinement process are generally used as the core material. Here, stress relief annealing is a heat treatment to relieve strain that is inevitably introduced by bending processes, etc., to turn grain-oriented electrical steel sheets into wound cores. This strain differs from the strain introduced by the magnetic domain refinement process and has a negative effect on iron loss.

[0006] Here, non-heat-resistant magnetic domain refinement treatment using an electron beam is generally performed in a vacuum space (hereinafter also referred to as a vacuum chamber), and from the viewpoint of productivity, it is performed by irradiating the electron beam onto the steel sheet while it is being threaded at a certain speed. However, when non-heat-resistant magnetic domain refinement treatment is performed using an electron beam, there is a correlation between the sheet threading speed, the pressure in the vacuum chamber (hereinafter also referred to as the degree of vacuum), and the iron loss of the grain-oriented electrical steel sheet that has been subjected to this treatment (domain refined grain-oriented electrical steel sheet). As the sheet threading speed increases, the pressure in the vacuum chamber increases (the degree of vacuum decreases), and the iron loss of the domain refined grain-oriented electrical steel sheet tends to deteriorate.

[0007] If the iron loss of domain-refined grain-oriented electrical steel sheet deteriorates, it will no longer be able to meet the required properties for use as an iron core material, resulting in a decrease in yield, so it is important to maintain a low pressure (high degree of vacuum) inside the vacuum chamber.In addition, if the sheet threading speed is slow, productivity will decrease, so it is important to make the sheet threading speed as fast as possible.

[0008] Generally, surface-adsorbed gases such as HO and O2 are present on the surface of steel sheets at invisible levels, and these surface-adsorbed gases (especially HO) are desorbed within the vacuum chamber. In other words, surface-adsorbed gases such as HO are brought into the vacuum chamber as the steel sheet passes through. When this happens, as the sheet passing speed increases, the amount of surface-adsorbed gases brought into the vacuum chamber increases, and it is thought that the evacuation capacity of the vacuum pump will gradually be unable to keep up, causing a decrease in the degree of vacuum.

[0009] Furthermore, if impurities such as H2O increase in the vacuum chamber and the degree of vacuum decreases, the irradiated electron beam has more opportunities to interfere with the impurities, making the amount of electron beam reaching the steel sheet unstable, which is thought to result in a decrease in the iron loss of magnetic domain refined grain-oriented electrical steel sheet.

[0010] Furthermore, not only when magnetic domain refinement treatment is performed on grain-oriented electrical steel sheets, but also when physical vapor deposition is performed in a vacuum chamber on a steel sheet production line, depending on the sheet passing speed, gases such as H2O and O2 adsorbed to the surface may not be completely removed, resulting in a decrease in the degree of vacuum in the vacuum chamber, which can reduce the purity and uniformity of the deposited film.

[0011] To address this issue, Patent Document 6 states that by heating the steel sheet to 50°C or higher using a heating device before it reaches the vacuum chamber where the magnetic domain refinement treatment is performed, it is possible to remove HO adsorbed to the steel sheet surface and maintain the degree of vacuum even when the sheet passing speed increases, thereby preventing a decrease in iron loss. Furthermore, if the magnetic domain refinement treatment is performed in the vacuum chamber while the steel sheet is still heated to 50°C or higher, the thermal strain introduced by the electron beam decreases and iron loss deteriorates, so it is possible to prevent a deterioration in iron loss by cooling the steel sheet to below 50°C using a cooling device before it enters the vacuum chamber. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-77380 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-129135 [Patent Document 3] Japanese Patent Application Publication No. 62-86121 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-172191 [Patent Document 5] Japanese Patent Application Publication No. 7-192891 [Patent Document 6] Japanese Patent Application Publication No. 2017-166016 Summary of the Invention [Problem to be solved by the invention]

[0013] To maintain a high degree of vacuum in the vacuum chamber regardless of the strip threading speed, it is necessary to quickly exhaust gases such as H2O that are absorbed by the steel strip and adsorbed to the surface. In other words, increasing the pumping capacity of the vacuum pump is effective. However, increasing the pumping capacity of the vacuum pump requires a significant increase in cost.

[0014] Furthermore, as described in Patent Document 6, when a steel sheet is heated and cooled, thermal stress occurs due to temperature deviation, and the steel sheet buckles, making it impossible to thread, or if the degree of buckling is large, the steel sheet may interfere with equipment and break. When a steel sheet becomes impossible to thread or breaks, it takes time to restore the steel sheet production line, resulting in a problem of reduced production efficiency.

[0015] The present invention has been made in view of the above circumstances, and has an object to provide a steel sheet manufacturing method and manufacturing equipment in a production line having a vacuum chamber through which steel sheets pass, which is capable of removing gases adsorbed on the surface of steel sheets brought into the vacuum chamber without heating and / or cooling the steel sheets. [Means for solving the problem]

[0016] The present invention provides the following. [1] In a production line having a vacuum chamber through which steel plates pass, Upstream of the vacuum chamber, the steel sheet is irradiated with far ultraviolet light containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm 2The method for manufacturing steel sheets includes the above irradiation. [2] In a production line having a vacuum chamber through which grain-oriented electrical steel sheets that have undergone final annealing pass, Upstream of the vacuum chamber, the grain-oriented electrical steel sheet that has been subjected to final annealing is irradiated with far ultraviolet light containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm. 2 Irradiate as above, then a method for producing a domain refined grain-oriented electrical steel sheet, the method including irradiating the grain-oriented electrical steel sheet that has been subjected to final annealing with an electron beam in the vacuum chamber to perform a magnetic domain refinement treatment; [3] The method for producing a magnetic domain refined grain-oriented electrical steel sheet according to [2], wherein the grain-oriented electrical steel sheet that has been subjected to final annealing has a surface that is subjected to tension coating. [4] A vacuum chamber through which the steel plate passes; a far-ultraviolet irradiator installed upstream of the vacuum chamber and irradiating the steel sheet with far-ultraviolet rays; A steel plate manufacturing facility having the above structure. [5] The far-ultraviolet irradiator emits far-ultraviolet rays containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm 2 The steel plate manufacturing equipment described in [4], which performs irradiation as described above. [6] A vacuum chamber through which grain-oriented electrical steel sheets that have undergone final annealing pass; an electron gun that irradiates the grain-oriented electrical steel sheet that has been subjected to final annealing and that passes through the vacuum chamber with an electron beam; a far-ultraviolet irradiator that is installed upstream of the vacuum chamber and irradiates the grain-oriented electrical steel sheet that has been subjected to final annealing with far-ultraviolet rays; This facility is capable of manufacturing magnetic domain refined grain-oriented electrical steel sheets. [7] The far-ultraviolet irradiator emits far-ultraviolet rays containing wavelengths of 200 nm or less at an integrated illuminance of 150 mJ / cm 2 The manufacturing equipment for magnetic domain refined grain-oriented electrical steel sheet according to [6], which performs irradiation as described above. [8] The manufacturing equipment for magnetic domain refined grain-oriented electrical steel sheet according to [6] or [7], which has differential pressure chambers on both the inlet and outlet sides of the vacuum chamber. [Effects of the Invention]

[0017] According to the present invention, in a production line having a vacuum chamber through which steel sheets pass, gases adsorbed on the surface of steel sheets brought into the vacuum chamber can be removed without heating and / or cooling the steel sheets.

[0018] According to the present invention, in a steel sheet production line having a vacuum chamber, by removing gas adsorbed to the surface of the steel sheet without heating or cooling the steel sheet using a heating device or a cooling device, it is possible to suppress a decrease in and variation in the degree of vacuum within the vacuum chamber. This improves the accuracy of the treatment performed within the vacuum chamber, and for example, it is possible to suppress deterioration in iron loss of grain-oriented electrical steel sheet that undergoes magnetic domain refinement treatment within the vacuum chamber.

[0019] Furthermore, it is possible to prevent the steel sheet from buckling due to heating or cooling, making it impossible to thread, or from interfering with equipment due to buckling, thereby preventing a decrease in productivity due to impossibility of threading, breakage of the steel sheet, etc. According to the present invention, there is no need to intentionally increase the exhaust capacity of the vacuum pump in order to maintain a high degree of vacuum in the vacuum chamber, and it is possible to prevent an increase in the production cost of the steel sheet. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing an example of manufacturing equipment for a domain-refined grain-oriented electrical steel sheet. [Figure 2] FIG. 2 is a diagram showing the absorption spectrum of H2O. [Figure 3] FIG. 3 is a diagram showing the relationship between the sheet passing speed and the degree of vacuum in the vacuum chamber. [Figure 4] FIG. 4 is a diagram showing the relationship between the sheet running speed and the iron loss of a domain refined grain-oriented electrical steel sheet. [Figure 5] FIG. 5 is a diagram showing the relationship between the integrated illuminance of far ultraviolet light and the degree of vacuum. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment shown below exemplifies an apparatus and a method for embodying the technical concept of the present invention, and the present invention is not limited to the following embodiment.

[0022] (steel plate) The steel sheet targeted by the present invention is preferably a thin steel sheet. Here, a thin steel sheet is a steel sheet having a thickness of 0.15 mm or more and 3.0 mm or less. The steel sheet also includes a steel strip. The chemical composition of the steel sheet can be appropriately selected depending on the application. An example of a grain-oriented electrical steel sheet will be shown below.

[0023] (Grain-oriented electrical steel sheet) In this embodiment, the chemical composition of the slab for grain-oriented electrical steel sheet is not particularly limited as long as it is a chemical composition that allows secondary recrystallization. Furthermore, when an inhibitor is used, for example, when an AlN-based inhibitor is used, it is sufficient to add appropriate amounts of Al and N, and when an MnS·MnSe-based inhibitor is used, it is sufficient to add appropriate amounts of Mn and Se and / or S. Of course, both inhibitors may be used in combination. In this case, the preferred contents of Al, N, S, and Se are, respectively, 0.01 to 0.065 mass% Al, 0.005 to 0.012 mass% N, 0.005 to 0.03 mass% S, and 0.005 to 0.03 mass% Se.

[0024] Furthermore, grain-oriented electrical steel sheets may be those in which the contents of Al, N, S, and Se are limited and no inhibitor is used. In this case, the amounts of Al, N, S, and Se are preferably controlled to less than 100 ppm by mass of Al, less than 50 ppm by mass of N, less than 50 ppm by mass of S, and less than 50 ppm by mass of Se, respectively.

[0025] Next, the basic components and optional additional components of the slab for the grain-oriented electrical steel sheet will be specifically described.

[0026] C: 0.08% by mass or less C is added to improve the hot-rolled sheet structure. However, if the C content exceeds 0.08 mass%, it becomes difficult to reduce the C content to 50 mass ppm or less, at which point magnetic aging does not occur during the manufacturing process, so the C content is preferably 0.08 mass% or less. Note that there is no need to set a lower limit for the C content, as secondary recrystallization is possible even in materials that do not contain C. In other words, the C content may be 0 mass%. When C is added to improve the hot-rolled sheet structure, the C content is preferably 0.01 mass% or more.

[0027] Si:2.0~8.0% by mass Silicon is an element effective in increasing the electrical resistance of steel and improving iron loss, and for this reason, the Si content is preferably 2.0% by mass or more. On the other hand, if the Si content is 8.0% by mass or less, it becomes easier to prevent a decrease in workability and a decrease in magnetic flux density. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

[0028] Mn:0.005~1.0% by mass Mn is an element necessary for improving hot workability, and therefore its content is preferably 0.005% by mass or more. On the other hand, if the Mn content is 1.0% by mass or less, it is easy to suppress a decrease in the magnetic flux density of the product sheet. Therefore, the Mn content is preferably in the range of 0.005 to 1.0% by mass.

[0029] The slab for grain-oriented electrical steel sheet preferably has the above-mentioned components as its basic components. In addition to the above-mentioned basic components, the slab may optionally contain the following elements. The following elements are effective in improving magnetic properties. One or more selected from Ni: 0.03 to 1.50 mass%, Sn: 0.01 to 1.50 mass%, Sb: 0.005 to 1.50 mass%, Cu: 0.03 to 3.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, and Cr: 0.03 to 1.50 mass%

[0030] Ni is an element useful for improving the hot-rolled sheet structure and enhancing magnetic properties, and it is preferable to contain 0.03% by mass or more of Ni. On the other hand, if the Ni content is 1.50% by mass or less, it is possible to prevent secondary recrystallization from becoming unstable, and it is easy to reduce the risk of deterioration of the magnetic properties of the product sheet. Therefore, if Ni is contained, the Ni content is preferably in the range of 0.03 to 1.50% by mass.

[0031] Furthermore, Sn, Sb, Cu, P, Mo, and Cr are also elements useful for improving magnetic properties, and when the content of each element is equal to or greater than the lower limit of the above-mentioned element, the effect of improving magnetic properties is more likely to be achieved. On the other hand, when the content of each element is equal to or less than the upper limit of the above-mentioned element, the risk of inhibiting the development of secondary recrystallized grains is more likely to be reduced. Therefore, when Sn, Sb, Cu, P, Mo, and Cr are contained, the content of each of the above elements is preferably set within the above-mentioned range.

[0032] The balance other than the above components is Fe and unavoidable impurities.

[0033] Next, a method for producing grain-oriented electrical steel sheet will be described. A slab having the above-mentioned composition is heated in a conventional manner and subjected to hot rolling. In this case, the slab may be hot rolled immediately after casting without heating. In the case of a thin cast slab, hot rolling may be performed, or the hot rolling may be omitted and the subsequent steps may be carried out directly.

[0034] Furthermore, if necessary, hot-rolled sheet annealing is performed. At this time, in order to highly develop the Goss structure in the product sheet, the hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100°C. That is, if the hot-rolled sheet annealing temperature is less than 800°C, the band structure from hot rolling remains, making it difficult to realize a grain-regulated primary recrystallization structure, and the development of secondary recrystallization may be inhibited. On the other hand, if the hot-rolled sheet annealing temperature exceeds 1100°C, the grain size after hot-rolled sheet annealing becomes too coarse, making it extremely difficult to realize a grain-regulated primary recrystallization structure.

[0035] After annealing the hot-rolled sheet, it is cold-rolled once or twice or more times with intermediate annealing in between, then recrystallization annealing is performed and an annealing separator is applied. After the annealing separator is applied, final annealing is performed for the purpose of secondary recrystallization and the formation of a forsterite film.

[0036] After the final annealing, it is preferable to perform flattening annealing to correct the shape. Furthermore, it is preferable to apply an insulating coating to the surface of the steel sheet before or after the flattening annealing. This insulating coating refers to a coating that can impart tension to the steel sheet in order to reduce iron loss (hereinafter also referred to as tension coating). Examples of this tension coating include inorganic coatings containing silica and ceramic coatings formed by physical vapor deposition, chemical vapor deposition, etc.

[0037] Through the above steps, a grain-oriented electrical steel sheet that has been subjected to final annealing is obtained.

[0038] (Steel plate manufacturing equipment) Next, the steel sheet manufacturing equipment of the present invention will be described. The manufacturing equipment of the present invention has a far-ultraviolet ray irradiation device and a vacuum chamber, in this order, along a steel sheet (steel strip) manufacturing line (threading line). That is, the manufacturing equipment of the present invention has a vacuum chamber through which the steel sheet passes and a far-ultraviolet ray irradiation device installed upstream of the vacuum chamber.

[0039] The far-ultraviolet irradiator irradiates far-ultraviolet rays onto the steel sheet passing through the sheet threading line. Then, in the vacuum chamber, the steel sheet irradiated with far-ultraviolet rays by the far-ultraviolet irradiator is subjected to various treatments (surface treatment, etc.) to produce a steel sheet (surface-treated steel sheet, etc.). Examples of such treatments include vacuum deposition treatment. When the steel sheet passing through the sheet threading line is a grain-oriented electrical steel sheet, examples of such treatments include magnetic domain refinement treatment. Note that a vacuum refers to a space with a pressure lower than atmospheric pressure. The pressure (degree of vacuum) within the vacuum chamber is adjusted appropriately depending on the treatment to be performed within the vacuum chamber, but can be set to 0.5 Pa or less, for example.

[0040] Hereinafter, a manufacturing facility for producing a magnetic domain refined grain-oriented electrical steel sheet will be described as an example.

[0041] Fig. 1 is a schematic diagram showing an example of manufacturing equipment for magnetic domain refined grain-oriented electrical steel sheet. The manufacturing equipment shown in Fig. 1 has, in this order, a far-ultraviolet irradiator 6 and a vacuum chamber 1 along a manufacturing line (sheet threading line) for grain-oriented electrical steel sheet (steel sheet S) that has undergone final finish annealing. That is, the manufacturing equipment shown in Fig. 1 has a vacuum chamber 1 through which the grain-oriented electrical steel sheet (steel sheet S) that has undergone final finish annealing passes, and a far-ultraviolet irradiator 6 installed upstream of the vacuum chamber 1. In addition, an electron gun 3 is installed in the vacuum chamber 1, which irradiates the steel sheet S passing through the vacuum chamber 1 with an electron beam.

[0042] Furthermore, as shown in FIG. 1, when magnetic domain refinement treatment is performed on a steel sheet S in a vacuum chamber 1, it is preferable to provide differential pressure chambers (inlet-side differential pressure chamber 2a and outlet-side differential pressure chamber 2b) on the inlet and outlet sides of the vacuum chamber 1, respectively. When differential pressure chambers are provided on the inlet and outlet sides of the vacuum chamber 1, there is no limit to the number thereof. One differential pressure chamber may be provided on each side of the vacuum chamber 1, or multiple differential pressure chambers may be provided on each side. The number of inlet-side differential pressure chambers and outlet-side differential pressure chambers may be the same or different. The internal pressure of the inlet-side differential pressure chamber 2a and the outlet-side differential pressure chamber 2b is adjusted to be lower than atmospheric pressure and higher than that of the vacuum chamber 1. This allows the pressure of the environment through which the steel sheet S passes to be adjusted in stages.

[0043] The manufacturing facility shown in FIG. 1 also includes a payoff reel 4 that dispenses the steel sheet S, and a tension reel 5 that takes up the magnetic domain refined grain-oriented electrical steel sheet that has been subjected to magnetic domain refinement processing in the vacuum chamber 1.

[0044] (Steel plate manufacturing method) The method for manufacturing steel sheets will be described below. Here, we will explain the case where grain-oriented electrical steel sheets are manufactured using the manufacturing equipment shown in Figure 1.

[0045] In this embodiment, the grain-oriented electrical steel sheet (steel sheet S) that has been subjected to final annealing and manufactured as described above is paid off from the payoff reel 4 and wound onto a tension reel 5, and the steel sheet S is passed through the vacuum chamber 1. In this embodiment, the surface of the steel sheet S is irradiated with far-ultraviolet rays from a far-ultraviolet irradiation device 6 that is installed upstream of the vacuum chamber 1 and between the payoff reel 4. As the steel sheet S that has been irradiated with far-ultraviolet rays reaches the inlet-side differential pressure chamber 2a provided on the inlet side of the vacuum chamber 1, adsorbed gas (HO) adhering to the steel sheet S is removed. This removes moisture that is brought into the vacuum chamber 1 by the steel sheet S and that causes fluctuations in the degree of vacuum. This improves the accuracy of processing within the vacuum chamber 1.

[0046] The far-ultraviolet rays have a wavelength of 200 nm or less. Preferably, the far-ultraviolet rays have a wavelength of 10 nm or more. In this embodiment, the surface of the steel sheet is irradiated with such far-ultraviolet rays to remove HO adsorbed on the surface of the steel sheet, which is a cause of fluctuations in the degree of vacuum, before the steel sheet reaches the vacuum chamber 1.

[0047] Figure 2 shows the absorption spectrum of HO from far-infrared to far-ultraviolet rays. As shown in Figure 2, HO has almost no absorption bands for light in the wavelength range of approximately 300 nm to 2500 μm, known as ultraviolet, visible light, or near-infrared light. However, compared to its absorption strength in these wavelength ranges, HO's absorption strength for light in the wavelength range of approximately 200 nm or less, known as far-ultraviolet light, is more than 10 times stronger. In addition, the energy of light generally depends on wavelength, with the shorter the wavelength, the greater the energy. When far-ultraviolet rays of this wavelength are irradiated onto a steel sheet, HO adsorbed on the surface of the steel sheet absorbs the far-ultraviolet rays and becomes excited, which can promote desorption from the steel sheet surface.

[0048] In this embodiment, a far-ultraviolet irradiation device equipped with a light source capable of irradiating such far-ultraviolet rays is used. The light source is not particularly limited, but examples include low-pressure mercury lamps and excimer lamps. Low-pressure mercury lamps have main emission peaks at 185 nm and 254 nm. On the other hand, excimer lamps have peaks at essentially only specific wavelengths, depending on the type of rare gas enclosed in the lamp. For example, Xe gas has an emission peak at 172 nm, and Ar gas has an emission peak at 126 nm. Furthermore, by using a light source filter such as a bandpass filter with such a light source, it is possible to irradiate only far-ultraviolet rays of a single wavelength or a specific wavelength range. Using a bandpass filter can further suppress the temperature rise of the steel sheet due to ultraviolet radiation.

[0049] In addition, due to the recent tightening of regulations on mercury, it is currently preferable to use an excimer lamp as the light source. Also, from the viewpoint of efficiently removing H2O adsorbed on the steel sheet, the integrated illuminance of far ultraviolet light is set to 150 mJ / cm2. 2 This means that the cumulative illuminance is 150 mJ / cm or more. 2 This is because if the temperature is above this level, the effect of removing H2O adsorbed on the steel sheet surface can be sufficiently achieved. Here, the integrated illuminance is the illuminance (unit: mW / cm2) which is the light intensity per unit area of ​​the steel sheet. 2 ) multiplied by the irradiation time (unit: s).

[0050] A commercially available irradiance meter can be used to measure the irradiance. It is preferable to use a product with spectral sensitivity in the required wavelength range as the measurement probe of the irradiance meter. In this embodiment, the distance between the position on the line along which the steel sheet passes and the light source is measured, and the value measured by separately arranging the light source and the measurement probe at the same distance is used as the irradiance.

[0051] Furthermore, since far-ultraviolet rays are absorbed and attenuated in the atmosphere, it is preferable to irradiate them in a vacuum. Therefore, it is preferable that the far-ultraviolet irradiation device is equipped with a vacuum chamber and that the above-mentioned light source is located within the vacuum chamber. Furthermore, the light source of the far-ultraviolet irradiation device may be located either above or below the steel sheet that is fed horizontally. Alternatively, it may be located both above and below the steel sheet to enhance the HO removal effect by far-ultraviolet irradiation. Note that when the steel sheet is fed vertically, the light source may be located on either the left or right side of the steel sheet, or on both sides. That is, far-ultraviolet rays may be irradiated on one side of the steel sheet, or on both sides of the steel sheet.

[0052] Furthermore, the distance between the light source of the far-ultraviolet irradiation device and the steel sheet (steel sheet surface) is preferably 1 mm or more and 10 mm or less. By setting the distance to 1 mm or more, it is possible to reduce the risk of the light source coming into contact with the steel sheet and being damaged when the steel sheet vibrates during passing. Furthermore, if the distance is 10 mm or less, it is possible to prevent the far-ultraviolet rays from attenuating before reaching the steel sheet surface, thereby further enhancing the effect of removing HO. Note that when far-ultraviolet rays are irradiated in the atmosphere, it is preferable that the distance between the light source and the steel sheet be 1 mm or more and 3 mm or less. The reasons for this are the same as those described above.

[0053] In the method for producing a magnetic domain refinement grain-oriented electrical steel sheet according to this embodiment, after the above-described far-ultraviolet irradiation, a magnetic domain refinement treatment is carried out using an electron beam in a vacuum chamber 1. The electron beam irradiation conditions used here may be conventionally known irradiation conditions, such as an acceleration voltage of 10 to 200 kV, a beam current of 0.1 to 100 mA, a beam scanning speed of 1 to 200 m / s, an irradiation point spacing in the direction perpendicular to the rolling direction of 0.01 to 1.0 mm, and an irradiation line spacing in the rolling direction of 1 to 20 mm.

[0054] A method for producing a steel sheet according to one embodiment of the present invention comprises, in a production line having a vacuum chamber through which a steel sheet passes, a far-ultraviolet irradiation step of irradiating the steel sheet with far-ultraviolet rays upstream of the vacuum chamber. It may also comprise, after the above step, a treatment step of subjecting the steel sheet to a treatment (such as a surface treatment) in the vacuum chamber. A method for producing a magnetic domain refined grain-oriented electrical steel sheet according to one embodiment of the present invention comprises, in a production line having a vacuum chamber through which a grain-oriented electrical steel sheet that has undergone final finish annealing passes, a far-ultraviolet irradiation step of irradiating the grain-oriented electrical steel sheet that has undergone final finish annealing with far-ultraviolet rays upstream of the vacuum chamber. It may also comprise, after the above step, an electron beam irradiation step of irradiating the grain-oriented electrical steel sheet that has undergone final finish annealing with an electron beam in the vacuum chamber to perform a magnetic domain refinement treatment.

[0055] Below, we explain an experiment conducted to confirm whether it is possible to improve iron loss variation by irradiating steel sheets with far-ultraviolet rays in the manufacture of grain-oriented electrical steel sheets in which magnetic domains are refined by electron beam irradiation. The experiment was conducted using the manufacturing equipment shown in Figure 1. The light source for the far-ultraviolet irradiation equipment was a xenon lamp filled with Ar, which has an emission peak at a wavelength of 172 nm. The steel sheets were irradiated with far-ultraviolet rays in a vacuum, with the distance between the steel sheets and the light source set at 3 mm.

[0056] <Experiment 1> A 0.30 mm thick grain-oriented electrical steel sheet that had undergone final annealing was threaded. Then, in a vacuum chamber 1, it was irradiated with an electron beam under conditions of an acceleration voltage of 120 kV, a current of 20 mA, a scanning speed of 150 m / s, an irradiation spot spacing of 0.32 mm in the direction perpendicular to the rolling direction, and an irradiation line spacing of 5 mm in the rolling direction, to perform magnetic domain refinement. The steel sheet threading speed was varied within the range of 20 to 200 m / min, and the relationship between the pressure (degree of vacuum) in the vacuum chamber 1 and the threading speed on the iron loss of the produced magnetic domain-refined grain-oriented electrical steel sheet was investigated. Because the iron loss value varies depending on the magnetic flux density level, steel sheets with the same magnetic flux density level (B8 = 1.93 T) were used for evaluation.

[0057] Figure 3 shows the relationship between the sheet passing speed and the degree of vacuum (average degree of vacuum) when multiple steel sheets were passed at that speed. The variation in the degree of vacuum when multiple steel sheets were passed at the same passing speed was also evaluated. The error bars in the plot of the degree of vacuum in Figure 3 indicate the standard deviation.

[0058] As shown in Figure 3, the vacuum level in vacuum chamber 1 did not change significantly at strip speeds below 100 m / min. However, as the strip speed exceeded 100 m / min, the pressure increased and the vacuum level tended to decrease. This is thought to be due to the large amount of moisture carried over from the steel sheet, which meant that the existing vacuum pumps could not keep up with the increased strip speed. Furthermore, even at the same strip speed, the vacuum level varied. This is thought to be due to the difference in the amount of moisture adhering to each steel sheet. Possible reasons for this variation in the amount of adhering moisture include the residence time and environment (high or low humidity environment, high or low humidity season, etc.) between the final annealing and electron beam irradiation. It was also observed that the variation in vacuum level tended to increase with increasing strip speed.

[0059] Next, Figure 4 shows the relationship between the strip running speed and the iron loss of the manufactured magnetic domain refined grain-oriented electrical steel sheet. Note that in Figure 4, the error bars in the plot of iron loss indicate the standard deviation. As shown in Figure 4, there is no significant change in iron loss at strip running speeds of 100 m / min or less, but iron loss tends to increase above 100 m / min. Furthermore, it was observed that the variation in iron loss tends to increase as the strip running speed increases. Furthermore, it was found that even at the same strip running speed, there was a variation in iron loss of ±0.02 W / kg or more. This relationship between strip running speed and iron loss was consistent with the relationship between strip running speed and vacuum level.

[0060] Therefore, we considered that controlling the degree of vacuum is important for stabilizing iron loss characteristics at a high level, and next investigated methods for stabilizing the degree of vacuum. First, when the degree of vacuum in the vacuum chamber 1 decreases (pressure increases), the iron loss characteristics of the magnetic domain refined grain-oriented electrical steel sheet processed in the vacuum chamber 1 deteriorate or their variability increases. This is due to an increase in the impurity concentration in the electron beam irradiation atmosphere. In other words, as the impurity concentration increases, the irradiated electron beam has more opportunities to interfere with the impurities, which is thought to destabilize the amount of electron beam reaching the steel sheet. Therefore, while maintaining a constant strip threading speed is effective for stabilizing the degree of vacuum, controlling the strip threading speed is unavoidable for achieving stable continuous strip threading. Changes in the degree of vacuum due to fluctuations in the strip threading speed are a significant factor in suppressing iron loss variability. In other words, suppressing fluctuations in the degree of vacuum is effective for suppressing iron loss variability.

[0061] <Experiment 2> Therefore, we investigated ways to suppress fluctuations in the degree of vacuum. Increasing the pumping capacity of the vacuum pump is an effective way to stabilize the degree of vacuum. However, increasing the pumping capacity of the vacuum pump would require a significant increase in cost, so this was ruled out as an option in this study. As mentioned above, the cause of the variation in the degree of vacuum is thought to be changes in the amount of moisture carried over onto the steel sheet, so we investigated ways to reduce this amount of moisture carried over. Specifically, after the coiled steel sheet was unloaded, it was irradiated with far-ultraviolet light containing wavelengths of 200 nm or less before reaching the vacuum chamber 1 for electron beam irradiation.

[0062] Figure 5 shows the relationship between the cumulative irradiance of far-ultraviolet rays irradiated upstream of the vacuum chamber 1, the degree of vacuum in the vacuum chamber 1, and the temperature of the steel sheet after irradiation with far-ultraviolet rays, at different sheet passing speeds. Figure 5(a) shows the experimental results for a sheet passing speed of 40 m / min, and Figure 5(b) shows the experimental results for a sheet passing speed of 150 m / min. The experimental conditions other than the far-ultraviolet rays irradiation conditions were the same as those in Experiment 1 above. The steel sheet temperature was measured by measuring the surface temperature of the steel sheet from after irradiation with far-ultraviolet rays until it reached the inlet differential pressure chamber 2a. Figure 5 shows that the cumulative irradiance of far-ultraviolet rays was 150 mJ / cm2 regardless of the sheet passing speed.2 It can be seen that the above measures can significantly reduce the absolute value and variations in the degree of vacuum in the vacuum chamber 1. Furthermore, there is almost no temperature rise in the steel sheet due to irradiation with far ultraviolet rays.

[0063] From the above experimental results, we have come to the conclusion that in order to stabilize the iron loss characteristics of magnetic domain refined grain-oriented electrical steel sheet manufactured by electron beam irradiation at a high level, it is important to carry out electron beam irradiation under the following conditions: After unwinding the coiled steel sheet (finish-annealed grain-oriented electrical steel sheet), the steel sheet was irradiated with far ultraviolet light containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm. 2 This removes as much moisture as possible from the steel sheet before it reaches the vacuum chamber where the electron beam is irradiated, suppressing the amount of moisture carried into the vacuum area and stabilizing the degree of vacuum at a high level. [Example]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0065] A steel slab containing 0.07% by mass of C, 3.45% by mass of Si, 0.05% by mass of Mn, 0.10% by mass of Ni, 240 ppm by mass of Al, 110 ppm by mass of N, 150 ppm by mass of Se, 12 ppm by mass of S, and 23 ppm by mass of O, with the remainder being Fe and unavoidable impurities, was produced by continuous casting, heated to 1410°C, and hot-rolled to a thickness of 2.5 mm, followed by hot-rolled sheet annealing at 1000°C for 30 seconds. Subsequently, the intermediate sheet was cold-rolled to a thickness of 2.0 mm, and intermediate annealing was performed under the conditions of an oxidation degree PHO / PHO = 0.39, a temperature of 1060°C, and a time of 100 seconds. The steel sheet was then pickled with hydrochloric acid to remove subscale from the surface, and cold-rolled again to produce a cold-rolled sheet with a thickness of 0.215 mm. The sheet was then subjected to decarburization annealing, with an oxidation degree of PH2O / PH2 = 0.47 and a soaking temperature of 840°C for 200 seconds. An annealing separator primarily composed of MgO was then applied, and final annealing was performed at 1220°C for 100 hours for the purposes of secondary recrystallization, forsterite film formation, and purification. An insulating coating solution containing colloidal silica and aluminum phosphate with a concentration of 60% by mass was then applied, followed by baking at 850°C for tension coating. This baking treatment also served as planarization annealing. In this manner, a grain-oriented electrical steel sheet with a tension coating and final annealing was produced.

[0066] After that, multiple grain-oriented electrical steel sheets that had undergone final annealing were passed through a vacuum chamber at different times and irradiated with an electron beam under three irradiation conditions in the vacuum chamber to perform magnetic domain refinement. The electron beam irradiation conditions were as shown in Table 1, and far-ultraviolet irradiation was carried out under various conditions upstream of the vacuum chamber (before reaching the inlet differential pressure chamber of the vacuum chamber). The light source for the far-ultraviolet irradiation device was a xenon lamp filled with Ar, which has an emission peak wavelength of 172 nm. The steel sheet was irradiated with far-ultraviolet rays in a vacuum, with the distance between the steel sheet and the light source set at 3 mm.

[0067] For comparison, an experiment was also conducted in which the far-ultraviolet irradiation device installed upstream of the vacuum chamber was replaced with a heating device. That is, instead of irradiating the steel sheet with far-ultraviolet rays, an experiment was conducted in which the steel sheet was heated, then introduced into a vacuum chamber and subjected to magnetic domain refinement treatment with an electron beam, thereby producing a magnetic domain refined grain-oriented electrical steel sheet. Another experiment was also conducted in which the steel sheet was introduced into a vacuum chamber and subjected to magnetic domain refinement treatment with an electron beam, without being irradiated with far-ultraviolet rays or heated upstream of the vacuum chamber, thereby producing a magnetic domain refined grain-oriented electrical steel sheet.

[0068] The steel sheet temperatures were measured using a thermoviewer immediately after removal from the payoff reel (listed as "before far-UV irradiation / before heating" in Table 1), immediately after far-UV irradiation or immediately after heating (listed as "after far-UV irradiation / after heating" in Table 1), and immediately before entering the inlet differential pressure chamber (listed as "immediately before differential pressure chamber" in Table 1). Table 1 also shows the average value of the vacuum level (average vacuum level) and the variation (standard deviation) of the vacuum level in the vacuum chamber where the magnetic domain refinement treatment was performed, as well as the average value of the iron loss (average iron loss level), the variation (standard deviation) of the iron loss, and the magnetic flux density of the manufactured magnetic domain refined grain-oriented electrical steel sheets.

[0069] [Table 1]

[0070] Among Nos. 1 to 4, which were manufactured under the same electron beam irradiation conditions in the vacuum chamber, Comparative Example No. 2 and Inventive Example No. 4 were manufactured under high-vacuum conditions with small variations in the vacuum level of the vacuum chamber. Therefore, compared to Comparative Example No. 1 (no treatment upstream of the vacuum chamber), iron loss variation was reduced, resulting in better results. On the other hand, Comparative Example No. 2 buckled during the sheet threading due to heating, making it impossible to thread. Sheets that buckled during the sheet threading process are marked with an "X" in the "Steel Sheet Shape" column in Table 1. Furthermore, Comparative Example No. 3 was unable to maintain a high vacuum level and could not suppress the vacuum level variation because the integrated irradiance of the far-ultraviolet light was outside the range of the present invention. Therefore, it was not possible to reduce the deterioration of the iron loss and iron loss variation of the magnetic domain refined grain-oriented electrical steel sheet.

[0071] Among Nos. 5 to 8, which were manufactured under the same electron beam irradiation conditions in the vacuum chamber, Comparative Example No. 6 and Inventive Example No. 8 were manufactured under high-vacuum conditions with small variations in the vacuum level of the vacuum chamber. Therefore, compared to Comparative Example No. 5 (no treatment upstream of the vacuum chamber), iron loss variation was reduced, resulting in better results. On the other hand, Comparative Example No. 6 buckled the steel sheet during threading due to heating, making it impossible to thread. Furthermore, Comparative Example No. 7 was unable to maintain a high vacuum level and could not suppress the vacuum level variation because the integrated irradiance of the far-ultraviolet light was outside the range of the present invention. Therefore, it was not possible to reduce the deterioration of iron loss and iron loss variation in the magnetic domain refined grain-oriented electrical steel sheet.

[0072] Among Nos. 9 to 12, which were manufactured under the same electron beam irradiation conditions in the vacuum chamber, Comparative Example No. 10 and Inventive Example No. 12 were manufactured under high-vacuum conditions with small variations in the vacuum level of the vacuum chamber. Therefore, compared to Comparative Example No. 9 (no treatment upstream of the vacuum chamber), iron loss variation was reduced, resulting in better results. On the other hand, Comparative Example No. 10 experienced sheet buckling during threading due to heating, making it impossible to thread. Furthermore, Comparative Example No. 11 was unable to maintain a high vacuum level and could not suppress vacuum level variation because the integrated irradiance of the far-ultraviolet rays was outside the range of the present invention. Therefore, it was not possible to reduce the deterioration of iron loss and iron loss variation in the magnetic domain refined grain-oriented electrical steel sheet. [Explanation of symbols]

[0073] 1 Vacuum chamber 2a Differential pressure chamber (inlet differential pressure chamber) 2b Differential pressure chamber (outlet differential pressure chamber) 3 Electron gun 4 Payoff Reel 5 Tension Reel 6 Far ultraviolet irradiation device

Claims

1. In a production line having a vacuum chamber through which steel sheets pass, Upstream of the vacuum chamber, the steel sheet is irradiated with far ultraviolet rays containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm ２ The method for manufacturing steel sheets includes the above irradiation.

2. In a production line having a vacuum chamber through which grain-oriented electrical steel sheets that have undergone final annealing are passed, Upstream of the vacuum chamber, the grain-oriented electrical steel sheet that has been subjected to final annealing is irradiated with far ultraviolet light containing wavelengths of 200 nm or less at an integrated irradiance of 150 mJ / cm ２ Irradiate as above, then a method for producing a domain refined grain-oriented electrical steel sheet, the method including irradiating the grain-oriented electrical steel sheet that has been subjected to final annealing with an electron beam in the vacuum chamber to perform a magnetic domain refinement treatment;

3. The method for producing a magnetic domain refined grain-oriented electrical steel sheet according to claim 2, wherein the grain-oriented electrical steel sheet that has been subjected to final annealing has a surface that has been subjected to tension coating.

4. a vacuum chamber through which the steel plate passes; a far-ultraviolet irradiator installed upstream of the vacuum chamber and irradiating the steel sheet with far-ultraviolet rays; A steel plate manufacturing facility having the above structure.

5. The far-ultraviolet ray irradiation device irradiates far-ultraviolet rays containing wavelengths of 200 nm or less with an integrated illuminance of 150 mJ / cm ２ The steel sheet manufacturing facility according to claim 4, wherein irradiation is performed in the above manner.

6. a vacuum chamber through which grain-oriented electrical steel sheets that have undergone final annealing pass; an electron gun that irradiates the grain-oriented electrical steel sheet that has been subjected to final annealing and that passes through the vacuum chamber with an electron beam; a far-ultraviolet irradiator that is installed upstream of the vacuum chamber and irradiates the grain-oriented electrical steel sheet that has been subjected to final annealing with far-ultraviolet rays; This facility is capable of manufacturing magnetic domain refined grain-oriented electrical steel sheets.

7. The far-ultraviolet ray irradiation device irradiates far-ultraviolet rays containing wavelengths of 200 nm or less with an integrated illuminance of 150 mJ / cm ２ The manufacturing equipment for a magnetic domain refined grain-oriented electrical steel sheet according to claim 6, wherein the irradiation is carried out in the above manner.

8. 8. The manufacturing facility for a magnetic domain refined grain-oriented electrical steel sheet according to claim 6, further comprising differential pressure chambers on both the inlet and outlet sides of the vacuum chamber.

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